Portion of a toothbrush



FIG. 1 is a right side view of a portion of a toothbrush showing my new design;

FIG. 2 is a left side view thereof;

FIG. 3 is a bottom view thereof; and,

FIG. 4 is a head end view thereof.

The broken line showing of three circular regions within the claim boundaries and the remainder of the toothbrush is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a portion of a toothbrush, as shown and described. 